Page - 997 - in Book of Full Papers - Symposium Hydro Engineering

embankment failure, a technical team organized to evaluate the internal erosion potential and risks. The potential of internal erosion through soil foundation can’t be completely modeled or analyzed, the probability of this phenomena occurrence were evaluated by using the soil foundation strata, sealing method of dam and foundation, the results of dam and foundation analyses in different loading conditions (in this paper, the analysis is limited to static loading condition), evaluation of hydraulic gradient and finally the dam and foundation behavior after reservoir filling. 2. DAM AND DAM SITE DESCRIPTION According to the geological studies, the right abutment of this dam is composed of two parts in terms of lithology. The upper part is weathered tuff in form of layered soils including clay, clayed sand and silty sand and then covered with variable thickness of fine-grained alluvial terraces (the thickness is between 3m and 20 m). The lower part is pyroxene andesite rock that is completely weathered and then moderate weathered pyroxene andesite. The foundation in left abutment is low to moderate weathering pyroxene andesite and consists of alluvial deposits of maximum 8.0 m thick in the middle of the valley. As it previously mentioned, the right abutment is critical due to its strata. Thus, in this paper, the right abutment is our subject. In order to determine the soil foundation strata, permeability and density of the soils, ground water table and finally geotechnical parameters for dam design, geotechnical investigation including field and laboratory tests in 6 boreholes and 7 test pits in this abutment was performed in the feasibility and detail design studies. According to the Unified Soil Classification System (USCS), and results of field and laboratory tests on the samples of the right abutment, the foundation soil is often in CL classification, soils with classification of SC, CH, SC-SM, SP- SM and SM have been observed as layer between soils with CL classification. The right abutment strata has been presented in Fig. 1. The fine grained soils of the right abutment is considered as dense and very dense soils based on the results of Standard Penetration Test (SPT), Since the No. of SPT tests (N) are more than 30 and 50. In order to determine the permeability coefficient of right abutment fine- grained material, lefrance tests were performed in one-meter stage with maximum 2.0 m intervals by using constant and falling head method. Corresponding to the results of lefrance tests, the average permeability coefficient of soils is 1.0e-6 cm/s and the variation of permeability coefficient is very low. Based on the lefrance tests, the right abutment fine-grained soils have been classified as low to very low permeable soils. The maximum hydraulic gradient is 25 degree toward to the Meshginchay River. The ground water level has been presented in Fig.1. 997